Nor Hapishah Abdullah

Influence of Milling Time on the Crystallization, Morphology and Magnetic Properties of Polycrystalline Yttrium Iron Garnet

The polycrystalline Yttrium Iron Garnet (YIG) powder with the chemical formula Y3Fe5O12 has been synthesized by using High Energy Ball Milling technique. The effect of various preparation parameters on the crystallinity, morphology and complex permeability of YIG, which includes milling time and annealing temperature were studied respectively by using XRD, SEM and Impedance Material Analyzer. The frequency dependence of complex permeability namely real permeability, µ’ and magnetic loss, µ’’ were measured at room temperature for samples sintered from 600°C to 1400°C, in the frequency range 10 MHz to 1 GHz. The results showed that milling time plays a role in determining the crystallinity of the milled powder where higher milling time results in better crystallinity due to high reactivity of the particles. From complex permeability measurement, it was observed that the initial permeability and magnetic loss increased with increasing grain size. The permeability values increased with annealing temperature and the absolute values of permeability decreased after attaining the natural resonance frequency of the material.

Influence of Microstructural Evolution on the Magnetically Group Dominance in Polycrystalline Y3Fe5O12 Multi-Samples

In present work, the effect of changing microstructure on magnetic properties which evolves in parallel, in particular from amorphous-to-crystalline development, in yttrium iron garnet was investigated. 9 toroidal samples of polycrystalline yttrium iron garnets were prepared by using the mechanical alloying technique and sintered at low to high sintering temperature for microstructure-dependent-magnetic evolutions. A brief, yet revealing characterization of the samples were carried out by using an X-ray Diffraction, Field Emission Scanning Electron Microscopy, Impedance Material Analyzer, LCR-meter and, Picoammeter. It is believed that microstructural features such as amorphous phase, grain boundary, secondary phase and intergranular pores contribute significant additional magnetic anisotropy and demagnetizing fields, thus affecting the initial permeability accordingly. A scrutinizing observation of the permeability component results show that they tend to fall into three groups of magnetic permeability according to degree of magnetic behaviour dominance. The Curie temperature remained relatively stable and unaffected by the evolution, thus confirming its intrinsic character of being dependent only on the crystal structure and compositional stoichiometry. The increased electrical resistivity while the microstructure was evolving is believed to strongly indicate improved phase purity and compositional stoichiometry.

A Hydrogen Gas Sensor Based on TiO 2 Nanoparticles on Alumina Substrate.

High demand of semiconductor gas sensor works at low operating temperature to as low as 100 °C has led to the fabrication of gas sensor based on TiO2 nanoparticles. A sensing film of gas sensor was prepared by mixing the sensing material, TiO2 (P25) and glass powder, and B2O3 with organic binder. The sensing film was annealed at temperature of 500 °C in 30 min. The morphological and structural properties of the sensing film were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The gas sensor was exposed to hydrogen with concentration of 100–1000 ppm and was tested at different operating temperatures which are 100 °C, 200 °C, and 300 °C to find the optimum operating temperature for producing the highest sensitivity. The gas sensor exhibited p-type conductivity based on decreased current when exposed to hydrogen. The gas sensor showed capability in sensing low concentration of hydrogen to as low as 100 ppm at 100 °C.

Dielectric properties of ceramic materials obtained from rice husk for electronic applications

This paper reports on dielectric properties of ceramic material obtained from Rice Husk (RH) for electronic applications. RH is considered as agriculture waste material, contains 20–25wt% of silica (SiO2). The nanometer-sized silica powder was prepared via mechanical alloying and subsequent molding into pellet form. The compacted pellet samples were sintered at 800°C, 1000°C, 1100°C and 1200 °C respectively. Silver paste was applied on both faces of the pellet to act as electrodes. For analysis of ferroelectric polarization with respect to electric field, measurement was done using ferroelectric hysteresis loop towards the sintered pellets. The dielectric analysis was done using LCR meter. It clearly shows that dielectric constant of the samples decrease with increasing applied frequency. The capacitance is found to be decreasing with increased sintering temperatures. The result showed that WHRA does contain silica which has high dielectric constant and therefore is suitable for electronics application.

Influence of Parallel Evolving Microstructure on Thermal Diffusivity in Strontium Titanate

This paper reports some research findings on the parallel evolutions of microstructural properties and thermal diffusivity in strontium titanate. Strontium titanate samples have been prepared via the high energy ball milling technique and subsequently moulded by a hydraulic pressing and followed by cold isostatic pressing. Nanometer-sized compacted powder samples were sintered from 500 to 1400°C using 100°C increments. Strontium titanate formation was observed at as early as 500°C sintering temperature alongside secondary phases. The full formation of strontium titanate was observed at 800°C sintering temperature and above. Average grain sizes showed a fluctuating trend with increased sintering temperatures due to carbonate decomposition at lower sintering temperatures (500 to 800°C) and grain growth phenomenon at higher sintering temperatures (900 to 1400°C). Parallel characterization of evolving thermal diffusivity showed the same trend of fluctuation at low sintering temperatures as indirect relationship but increased with increased grain size due to a lesser amount of phonon scattering. However, thermal diffusivity values decreased with increased temperatures because of increased phonon-phonon scattering.